We divide 451389 by 90
The aim is to understand the frequency of 90 in 451389.

Let's proceed to step 1:
When dividing 4 by 90, we get 0 with a remainder of 4.
Record the quotient 0 as the next digit in the result. 
Result so far: 0.0
Subtract 0 from 4 to get 4.
Fetch the next digit (5) from the dividend, attach it to 4 and continue: 45 / 90

Going ahead to step 2:
When dividing 45 by 90, we get 0 with a remainder of 45.
The next digit of our result is 0. 
Result so far: 0.0
Deduct 0 from 45 and we're left with 45.
Append the next digit (1) from the dividend to 45 and continue with: 451 / 90

Step 3:
451 divided by 90 is 5 with a remainder of 1.
Put 5 as the next digit of the answer. 
Result so far: 5.0
Subtract 450 from 451 to get 1.
Bring next digit (3) of the dividend behind the 1 and repeat the process: 13 / 90

Let's proceed to step 4:
90 can be fit into 13 0 times, resulting in a remainder of 13.
The next digit of our result is 0. 
Result so far: 50.0
Deduct 0 from 13 and we're left with 13.
Bring next digit (8) of the dividend behind the 13 and repeat the process: 138 / 90

Advancing to step 5:
90 goes into 138 1 times with a remainder of 48.
Use 1 as the next digit of our solution. 
Result so far: 501.0
Deduct 90 from 138 and we're left with 48.
Include the next digit (9) from the dividend after 48, then repeat: 489 / 90

Let's proceed to step 6:
489 divided by 90 is 5 with a remainder of 39.
Record the quotient 5 as the next digit in the result. 
Result so far: 5015.0
If we subtract 450 from 489, we get 39.
Since there are no more digits in the dividend, we add a zero to the remainder making it 390, and continue the process.

Let's proceed to step 7:
90 can be fit into 390 4 times, resulting in a remainder of 30.
The number 4 becomes the next digit in our result. 
Result so far: 5015.4
If we take 360 away from 390, we end up with 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

Step 8:
90 can be fit into 300 3 times, resulting in a remainder of 30.
The next digit of our result is 3. 
Result so far: 5015.43
If we subtract 270 from 300, we get 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

On to step 9:
If we divide 300 by 90, we get 3 and a remainder of 30.
Use 3 as the next digit of our solution. 
Result so far: 5015.433
If we subtract 270 from 300, we get 30.
Since there are no more digits in the dividend, we add a zero to the remainder making it 300, and continue the process.

The final outcome is 5015.433, with a leftover of 0.003.